Method of manufacturing a chain of filaments for filament lamps,discharge tubes or the like

ABSTRACT

The invention relates to a method of manufacturing a chain of filaments in which a wire which is wound on a mandril is expanded by means of two jaws to form a straight intermediate member. As a result of this the mandril breaks between the jaws. The part of the wire and the mandril which is present between the jaws is preferably heated by the passage of current.

United States Patent [191 Moeys et a1. 1

[ Aug. 13, 1974 METHOD OF MANUFACTURING A CHAIN OF FILAMENTS FOR FILAMENT LAMPS, DISCHARGE TUBES OR THE LIKE [75] Inventors: Gosuines Phillippus Guilielmus Moeys, Varese, Italy; Johannes Martinus Wittkamper, Amiens, France [73] Assignee: U.S. Philips Corporation, New

York, NY.

22 Filed: Feb. 26, 1973 21 Appl.N0.:335,944

[30] Foreign Application Priority Data Mar. 16, 1972 Netherlands 7203462 [52] U.S.Cl. 140/71.5,29/618 [51] Int. Cl B21f 3/04 [58] Field of Search 140/715, 71.6; 29/610,

[56] References Cited UNITED STATES PATENTS 2,247,869 7/1941 Beers i40/71.5 2,589,521 3/1952 Wheeler et a1. 29/618 3,035,148 5/1962 Oakley 219/68 3,401,723 9/1968 Petry 219/68 3,461,921 8/1969 Ackerman 140/715 Primary ExaminerLowell A. Larson Attorney, Agent, or Firm-Frank R. Trifari [5 7 ABSTRACT The invention relates to a method of manufacturing a chain of filaments in which a wire which is wound on a mandril is expanded by means of two jaws to form a straight intermediate member. As a result of this the mandril breaks between the jaws. The part of the wire and the mandril which is present between the jaws is preferably heated by the passage of current.

4 Claims, 6 Drawing Figures The invention relates to a method of manufacturing a chain of helically wound filaments for electric filament lamps, discharge tubes, or the like, which filaments are' connected by intermediate members, in which the starting material is a wire wound on a mandril, which mandril is subjected in a number of successive places to a severing treatment and which wire is expanded in said places in such manner that intermediate members are formed, the mandril which is divided into pieces being removed afterwards. Such a method is known.

In the known method the mandril is broken by means of a chisel which is driven into the mandril between two turns. Thestroke movement of the chisel should be so accurate that the mandril is broken without touching the wire. While one part of the mandril is held, the broken part of the mandril is forced away by the chisel. The wire which connects the two parts of the mandril is stretched. The drawback of this method is that it is not suitable in practice for manufacturing filaments having a very small wire diameter because the danger that the chisel does not only break the mandril but also breaks the wire becomes larger as the diameters of wire and mandril are chosen to be smaller.

It is an object of the invention to provide a method which does not exhibit the said drawback.

For that purpose the method according to the invention is characterized in that the mandril with the wire wound on it is exposed to the action of two clamping members engaging on either side of a severing place, said members being moved apart to such an extent that the mandril breaks at that area while forming an intermediate member.

Because the wire is wound helically across the mandril, the part of the wire which is present between the clamping member can easily be stretched. However, the mandril is solid, and will therefore break when the clamping members are moved apart while the wire is only stretched and forms an intermediate member.

Thermal energy is preferably applied to the part of the mandril and the wire present between the clamping members. The advantage of this is that a smaller pulling force is necessary for breaking the mandril.

A favourable embodiment of the method according to the invention is characterized in that the thermal energy is supplied by means of an electric current passed through the mandril and the wire, the clamping members being constructed as electrodes. Because the produced thermal energy is dissipated via the clamping members, the temperature of the mandril is highest centrally between the clamping members so that in said position the mandril is weakest and will preferably break at that area. As a result of this it is possible to produce a chain of filaments of the same length which are connected together by intermediate members of likewise the same length.

The clamping members, after breaking of the mandril are preferably moved further apart to form a straight intermediate member.

The invention furthermore relates to a chain of helically wound filaments for electric filament lamps, discharge tubes or the like, which filaments are connected together by intermediate members, manufactured by any of the above-described methods.

The invention furthermore relates to a helically wound filament which is provided with stretched ends and which has been obtained by severing the intermediate members occurring in the above-mentioned chain.

The invention will now be described in greater detail with reference to a drawing which shows an embodiment of the method according to the invention.

FIGS. 1a to 1e show the stages which can be distinguished in this embodiment.

FIG. 2 shows the temperature variation in the mandril upon heating by means of electric current.

As shown in FIG. 1a, starting material is a wire 1 of tungsten which is wound on a mandril 2. The mandril with the wire are clamped in the clamping members 3 As a result of this the mandril 2 is reduced in crosssection and breaks centrally between the jaws 3 and 4 and at thesame time the wire 1 is stretched so that an intermediate member 7 is formed. When the clamping members after breaking the mandril are moved further apart, the intermediate member 7 will assume a straight shape. In the subsequent state (1c) the clamping members 3 and 4 are opened, jaw 4 is moved in the direction of the arrow q until it assumes the position shown in 1a and the mandril is pulled between the clamping members in the direction denoted by the arrow r. The clamping members (1d) are then closed after which jaw 4 is again moved in the direction of the arrow p (1e).

In this manner a chain of mandril segments 5 is formed on which a number of turns occur, in this embodiment four turns, which are connected together by means of intermediate members 6 and 7. In a further stage the segments 5 are removed by means of an etching treatment. The chain is preferably left intact until after said etching treatment; the filaments are formed only on the lamp mounting machine by severing the intermediate members.

What is claimed is:

1. A method of manufacturing a chain of helically wound filaments for electric filament lamps, discharge tubes or the like, which filaments are connected by intermediate wire members comprising the steps of:

winding a wire on a mandril;

clamping the wire-wound mandril in two places with clamping members, said clamping places being disposed on either side of a predetermined location for separating said mandril;

separating said clamping members so as to break the mandril at said predetermined location; and

simultaneously forming said intermediate wire member.

2. A method as claimed in claim 1, wherein the separating step includes supplying thermal energy to the 3 4 part of the mandril and the wire present between the 4. A method as claimed in claim 1, wherein the Clamping membersclamping members, after breaking of the mandril, are

3. A method as claimed in claim 1, wherein the thermal energy is supplied by means of an electric current passed through the mandril and the wire, the clamping 5 membermembers being constructed as electrodes.

moved further apart to form a straight intermediate 

1. A method of manufacturing a chain of helically wound filaments for electric filament lamps, discharge tubes or the like, which filaments are connected by intermediate wire members comprising the steps of: winding a wire on a mandril; clamping the wire-wound mandril in two places with clamping members, said clamping places being disposed on either side of a predetermined location for separating said mandril; separating said clamping members so as to break the mandril at said predetermined location; and simultaneously forming said intermediate wire member.
 2. A method as claimed in claim 1, wherein the separating step includes supplying thermal energy to the part of the mandril and the wire present between the clamping members.
 3. A method as claimed in claim 1, wherein the thermal energy is supplied by means of an electric current passed through the mandril and the wire, the clamping members being constructed as electrodes.
 4. A method as claimed in claim 1, wherein the clamping members, after breaking of the mandril, are moved further apart to form a straight intermediate member. 